The invention relates to screw compressors and, more particularly, to a screw compressor and diffuser structure wherein kinetic losses are reduced.
The compression process in a screw compressor occurs within rotating pockets. Kinetic energy is imparted to compressed gases. To reduce dissipative effects of leakage in these machines, and to reduce their size and cost, it is desirable to run them at high tip speeds. The optimum tip speed of these machines depends among other factors, upon the relative balance between leakage losses, which decrease at high speeds, and viscous and kinetic losses, which increase at high speed. In an oil-less or near oil-less machine, the viscous losses are of minor concern, and tip speed is limited by kinetic losses which increase with the square of speed. Higher tip speeds could be obtained in screw compressors if part of the leaving kinetic energy could be efficiently recovered in an exit diffuser. This is done, for example, with turbo-compressors wherein the discharge flow is much better directed by the blades and flow distortion is tolerable.
Screw compressors, on the other hand, have a much more complex flow at their discharge port(s), with unfavorable flow directions and, possibly, high circulatory structure. The complex geometry of the discharge port relative to the rotors and housing makes it much more difficult to guide the flow efficiently to a diffuser throat. This is in part due to the highly tangential components of flow discharged in opposite tangential or radial directions from the two or more meshed rotors of the compressor.
It is clear that the need remains for an improved structure for guiding discharge flows from the compressor so as to improve compressor efficiency.
It is therefore the primary object of the present invention to provide such a structure.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
According to the invention, a screw compressor is provided which comprises a housing containing at least one rotor for generating a discharge flow in a discharge flow direction; a diffuser communicated with said housing and having a collecting portion for receiving said discharge flow, a diffuser throat and a diffuser portion, said diffuser extending from said housing in a diffuser direction; and at least one turning vane positioned in said collecting portion and adapted to guide flow from said discharge flow direction to said diffuser direction.